1. Field of the Invention
The present invention relates to a lens antenna apparatus utilizing a spherical lens that focuses radio beams, which is used in ground stations of a satellite communication system. More particularly, the invention relates to a lens antenna apparatus having a configuration suitable to be mounted on a mobile unit.
2. Description of the Related Art
Conventionally, a lens antenna apparatus utilizing a spherical lens capable of focusing radio beams has been developed. Radiators are arranged in given positions on the lower hemisphere of the spherical lens, and the directivity of the radiators are aligned with the center of the spherical lens to form radio beams in a given direction. The radio beams can be oriented everywhere in the celestial sphere only by freely moving the radiators on the lower hemisphere of the spherical lens. The lens antenna apparatus therefore has the advantage that it need not rotate as a whole unlike a parabolic antenna apparatus and its driving system can easily be downsized.
Under the present circumstances, however, the lens antenna apparatus is difficult to miniaturize further because of constraints of downsizing of the spherical lens in itself. Further, the apparatus is not easy to handle during assembly since it is spherical. To resolve these problems, the following hemispherical lens antenna apparatus is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publications Nos. 2002-232230and 2003-110352. An upper hemispherical lens, which is formed by halving a spherical lens, is placed on a radio reflector to focus radio waves from the celestial sphere, and the reflector reflects the radio waves, thus acquiring the radio waves on the outer surface of the hemispherical lens.
The hemispherical lens antenna apparatus has received attention as one mounted on a mobile unit since it is easy to miniaturize, whereas it needs to communicate with a plurality of stationary satellites on a stationary orbit. It is thus desirable to achieve a multibeam lens antenna apparatus having a simple and stable configuration.